The invention relates to a blind rivet as defined in the preamble to claim 1. The invention further relates to a method of producing a blind-rivet connection as defined in the preamble to claim 12.
A generic blind rivet is known under the brand name HEMLOK.RTM. from the catalogue 125.10101.88(00.00) of Avdel Verbindungselemente [Connecting Elements] GmbH. To produce a blind-rivet connection, the rivet shank of the known blind rivet is inserted into a flush bore of a plurality of components whose surfaces rest against one another until the set-head lies on the component surface. After the blind rivet has been inserted, the rivet shaft is tension-loaded counter to the insertion direction. The setting tool that produces the blind-rivet connection is supported on the set-head of the blind rivet. The widened shaft head transmits the tension loading of the rivet shaft onto the free end of the rivet shank, which projects beyond the surface of the components remote from the set-head. Because of the mechanical pressure on the rivet shank, the shank is deformed into a so-called closing head. The components to be riveted are now clamped between the set-head, on the one hand, and the closing head, on the other hand, and thus fixed to one another. In the known blind rivet, the shaft head pushes the free end of the rivet shank ahead of itself to form the closing head. This leads to a folding of the rivet shank. The closing head therefore has the shape of an annular ring. When the closing head is completely formed, the mechanical tension acting inside the rivet shaft increases abruptly. This causes the rivet shaft to break off at a break-off groove provided at a defined distance from the shaft head for this purpose. If the known blind rivet is used to rivet components having a varying total thickness, the rivet shaft is always separated in a different position with respect to the set-head end as a function of the respective component thickness. This is undesirable for visual as well as stability reasons. Furthermore, no mechanism for stopping the shaft remaining in the rivet shank against the set-head is provided in the known blind rivet. Particularly in dynamic stressing, this leads to instability of the known blind rivet, because the residual shaft only counteracts expansion of the rivet shank caused by frictional wear, or in transversal contraction of the rivet shank.
A further blind rivet of the aforementioned type is known under the name HUCK.RTM. MAGNA-BULB from the catalogue TITGEMEYER 0292 Tb1012 of GEBR. [Brothers] TITGEMEYER GmbH & Co KG. In this blind rivet, the shaft head has an annular projection that is formed onto the casing of the rivet shaft with spacing from the end of the shaft head. At a defined distance from the shaft head, the rivet shaft is again provided with a break-off groove. Moreover, a notch whose edge facing the shaft head projects radially beyond the edge remote from the shaft head to form a stop is provided between the break-off groove and the shaft head. With the MAGNA-BULB system, the closing head is again formed through the folding of the rivet shank into an annular ring. Here, however, the increase in tension that occurs following the formation of the closing head does not lead directly to the breaking off of the rivet shaft at the break-of point. Instead, the annular projection of the shaft head breaks off first. The annular projection is displaced toward a knurling provided at the end of the shaft head, which fixes the annular projection. In the MAGNA-BULB system, the rivet shaft does not break off at the break-off point until, with continuous pulling at the rivet shaft, the stop provided there is pressed against a corresponding stop of the rivet shank. The stops are arranged such that the rivet shaft is always separated flush with the set-head end. When seat-head material is pressed into the notch of the rivet shaft, the rivet shaft is simultaneously fixed to the set-head. A disadvantage, however, is that the rivet shaft and rivet shank are only fixed on the closing-head side through frictional lockup. This frictional-lockup connection is gradually relaxed in dynamic stressing, in particular, which leads to a worsening of the rivet connection.
In addition, the rivet-shaft material at the break-off edge of the annular projection is especially susceptible to corrosion. Because this break-off edge lies inside the annular shank, the danger exists of uncontrollable internal corrosion.
DE-PS 35 21 653 discloses a blind rivet whose rivet shaft is provided with a plurality of adjacent break-off grooves arranged axially in series. The set-head of the known blind rivet is embodied as an oblong sleeve that is widened in the region adjoining the rivet shank to form an approximately annular retaining collar. Starting from the retaining collar, the outer diameter of the sleeve-like set-head tapers approximately conically toward the set-head end. To produce the rivet connection, in the known blind rivet a setting tool having a tubular mouthpiece is used, which is pushed coaxially onto the sleeve-shaped set-head until the set-head rests in a form-fitting connection against the inside wall of the mouthpiece. The increase in tension that occurs after the closing head is formed effects a further displacement of the mouthpiece with respect to the sleeve-like set-head, with the set-head material being deformed radially inwardly. The set-head material thus fills the break-off grooves of the rivet shaft inside the set-head, thereby locking the rivet shaft with the set-head. The further increase in tension occurring as the mouthpiece impacts the wide retaining collar effects the breakage of the rivet shaft at a break-off groove ending approximately flush with the set-head end. The known blind rivet has the disadvantage that the sleeve-like set-head is forced to project far beyond the component surface. The known blind rivet can therefore only be used generally at inaccessible component surfaces, since the projecting set-head poses an injury threat for persons or a damage threat for adjacent objects, particularly at a component surface that is moved. A further disadvantage of the known blind rivet is that the mouthpiece is exposed to large radial forces during the pressing process. These radial forces, which act perpendicular to the tension direction, lead to a high material stress within the setting tool.
In a blind rivet known from DE-GM 83 27 405, the shaft head is hollow. The formation of the closing head is not effected by folding, but by a radial widening of the rivet shank. The hollow shaft head is simultaneously compressed and drawn, at least partially, into the rivet shank. Similarly to the MAGNA-BULB system, a flush breakage of the rivet shaft and an axial fixing of the residual shaft are assured by corresponding stops at the set-head and rivet shaft. A disadvantage of this arrangement is that, particularly with dynamic stressing, the rivet shank and the hollow shaft head are deformed in an inelastic manner. As a result, the rivet connection gradually relaxes. A further disadvantage of the known blind rivet is that its cross section does not completely fill the bore provided in the components because of the hollow shaft head drawn into the rivet shank. This impairs the stability of the rivet connection under shearing stress.